In drilling oil and gas wells, it is often necessary to isolate zones within a wellbore in order to achieve well control. Zones are typically isolated by setting packers or plugs at specified locations within the wellbore. These downhole tools can be used for a number of purposes. In the case of flow diversion, packers allow fluid to be diverted from the tool through perforations in the wellbore. Typically, composite plugs are used for temporary applications to plug a well. Most commonly they are used when a wellbore intersects multiple production zones. The terms “packer” and “plug” are used interchangeably herein.
Packer assemblies usually include an elastomeric material to seal the annulus and a slip assembly to secure the packer assembly against the casing. Typically, a slip assembly includes a slip and a cone or wedge, located about the mandrel, wherein the slip is used to grip the casing, typically by partially penetrating the casing wall. A slip will usually be a complete ring or segmented ring formation. The outer surface of the slip usually has sharp edges to bite the casing, which are made of a material harder than the casing in order to penetrate the casing. The inner edge of the slip may be biased to sit on the face of the cone, such that the slip can ride up the cone during the setting process. A packer assembly is set by using a setting tool to apply axial pressure to the assembly causing the slip and the cone to move towards each other in the longitudinal direction. As the slip and the cone move towards each other the slip is forced over the cone and moves radially outward to bite the casing.
With the advent of drillable bridge plugs and packers, such as composite or aluminum bridge plugs and packers, it has become desirable to minimize the amount of hard or otherwise difficult to drill material that may be utilized in a bridge plug or packer. Typically a composite or otherwise drillable bridge plug or packer is, as the name suggests, easily drillable. Unfortunately, the slip assembly, in order to function may be very hard and consequently very dense. Upon setting the slip assembly is forced radially outward, breaking the slip ring into smaller pieces. When it is time to drill out the bridge plug the drill or mill bit progresses to the location adjacent to the broken bits of the slip ring but the mud flow typically is not sufficient to circulate out all of the dense pieces of the slip ring therefore pieces of the slip ring fall towards the bottom of the well. The pieces of the slip ring then accumulate on the next lower bridge plug. The metal pieces may then be lodged in the drill or begin to rotate with the drill, causing difficulty in further drilling.
In order to prevent dense pieces of the slip rings from accumulating downhole, one solution is to utilize a composite or otherwise drillable and less dense slip ring and then embedding hardened teeth, such as ceramic or cermet teeth, into the slip ring. The hardened teeth are smaller and usually less dense or at least configured to maximize the surface area of each piece.
Typically when a ceramic or other hardened button is embedded in the slip ring, the sharp outer edges of the ceramic or hardened button can be damaged before the embedded button is fully set in the casing, reducing the ability of the embedded button to bite the casing. Additionally, when the bridge plug is being run into the wellbore, the outer edges of the slip or the embedded buttons may be chipped when the slip or buttons make contact with the casing. Typically, most of the damage to the edges of the slip occurs during setting when an embedded button may be moved longitudinally along the casing while partially embedded in the casing during the setting process.
When longitudinal pressure is first applied to the bridge plug or packer assembly, the slip ring and any embedded buttons are forced to move longitudinally along the cone while also moving radially outward. The radial movement of the slip ring will cause the embedded buttons to contact the casing. As more pressure is applied, the slip ring longitudinally along the cone, causing the outer edge of the embedded buttons to drag along the casing while digging further into the casing. This drag tends to cause the sharp edges of the embedded buttons or the slip ring to chip as the bridge plug or packer assembly moves to its final set position. This damage to the embedded buttons reduces the performance of the embedded buttons and the slip assembly in gripping the casing.
There is a need in the art to identify a way to prevent chipping of these buttons while reducing metallic content. This invention addresses this problem.